Coalesce async touch move events until the ack back from render

content/browser/renderer_host/input/touch_event_queue.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_BROWSER_RENDERER_HOST_INPUT_TOUCH_EVENT_QUEUE_H_
 #define CONTENT_BROWSER_RENDERER_HOST_INPUT_TOUCH_EVENT_QUEUE_H_
 
 #include <deque>
 #include <map>
 
@@ skipping 48 matching lines @@
   // single touch-move event). The event may also be immediately forwarded to
   // the renderer (e.g. when there are no other queued touch event).
   void QueueEvent(const TouchEventWithLatencyInfo& event);
 
   // Notifies the queue that a touch-event has been processed by the renderer.
   // At this point, the queue may send one or more gesture events and/or
   // additional queued touch-events to the renderer.
   void ProcessTouchAck(InputEventAckState ack_result,
                        const ui::LatencyInfo& latency_info);
 
+  void ProcessUncancelableTouchMoveAck();
+
   // When GestureScrollBegin is received, we send a touch cancel to renderer,
   // route all the following touch events directly to client, and ignore the
   // ack for the touch cancel. When Gesture{ScrollEnd,FlingStart} is received,
   // resume the normal flow of sending touch events to the renderer.
   void OnGestureScrollEvent(const GestureEventWithLatencyInfo& gesture_event);
 
   void OnGestureEventAck(
       const GestureEventWithLatencyInfo& event,
       InputEventAckState ack_result);
 
@@ skipping 16 matching lines @@
   bool empty() const WARN_UNUSED_RESULT {
     return touch_queue_.empty();
   }
 
   size_t size() const {
     return touch_queue_.size();
   }
 
   bool has_handlers() const { return has_handlers_; }
 
+  int PendingUncancelableEventAckCount() const {
+    return pending_uncancelable_event_ack_count_;
+  }
+
+  int SentUncancelableTouchMoveCount() const {
+    return sent_uncancelable_touch_move_count_;
+  }
+
  private:
   class TouchTimeoutHandler;
   class TouchMoveSlopSuppressor;
   friend class TouchTimeoutHandler;
   friend class TouchEventQueueTest;
 
   bool HasPendingAsyncTouchMoveForTesting() const;
   bool IsTimeoutRunningForTesting() const;
   const TouchEventWithLatencyInfo& GetLatestEventForTesting() const;
 
@@ skipping 80 matching lines @@
   // been preventDefaulted.
   scoped_ptr<TouchMoveSlopSuppressor> touchmove_slop_suppressor_;
 
   // Whether touch events should remain buffered and dispatched asynchronously
   // while a scroll sequence is active.  In this mode, touchmove's are throttled
   // and ack'ed immediately, but remain buffered in |pending_async_touchmove_|
   // until a sufficient time period has elapsed since the last sent touch event.
   // For details see the design doc at http://goo.gl/lVyJAa.
   bool send_touch_events_async_;
   scoped_ptr<TouchEventWithLatencyInfo> pending_async_touchmove_;
+
+  // Once this value is greater than 0, which means we should ignore the
+  // following ignore_ack_ numbers of acks from render for async touch moves.
+  int pending_uncancelable_event_ack_count_;
+
+  // For uncancelable touch moves, not only we send a fake ack, but also a real
+  // ack from render, which we use to decide when to send the next touch move.
+  // This can help avoid the touch event queue keep growing when render handles
+  // touchmove slow. We use sent_uncancelable_touch_move_count_ to count the
+  // number of uncancelable touch moves sent out are waiting for
+  // their acks back from render.
+  int sent_uncancelable_touch_move_count_;

[tdresser, 2015/03/25 14:16:18]

I'm still not clear on why we need both pending_uncancelable_event_ack_count_
and sent_uncancelable_touch_move_count_.

Let's talk it over in person.

   double last_sent_touch_timestamp_sec_;
 
   // Event is saved to compare pointer positions for new touchmove events.
   scoped_ptr<blink::WebTouchEvent> last_sent_touchevent_;
 
   DISALLOW_COPY_AND_ASSIGN(TouchEventQueue);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_INPUT_TOUCH_EVENT_QUEUE_H_